1. Field of the Invention
The present invention relates in general to a motorcycle, and more particularly to a relative arrangement of a fuel tank and an exhaust pipe in a motorcycle.
2. Description of the Prior Art
In a two-cycle engine, during a scavenging period the interior of an exhaust pipe is held at a negative pressure by an inertial effect of an exhaust gas within the exhaust pipe, thereby the exhaust gas is sucked to enhance scavenging efficiency. Provision is also made such that a positive pressure may be established at the position of an exhaust port just before the exhaust port is closed by making use of a reflection wave to push back fresh gas that is going to pass through. Improvement of an engine performance is thereby achieved.
The above-mentioned effect called "KADENACY-effect" can be realized by a special configuration of an exhaust pipe, and generally such configuration that the exhaust pipe expands gradually from its inlet, and after it has reached the maximum diameter, it contracts gradually, and is considerably narrowed at its outlet. FIGS. 1 to 3 show one example of a motorcycle equipped with the above-described exhaust pipe 01.
Exhaust pipe 01 has a predetermined length to provide the KADENACY-effect. For the purpose of effectively realizing the necessary length, it is bent with a large curvature from an exhaust inlet portion 02 connected to an exhaust port of an engine E, extends downwards, then extends in the widthwise direction of a vehicle body and, thereafter, extends to the rear of the vehicle body along the lower edge of one branch of a fuel tank 04 having a V-shaped cross-section which straddles a main frame 03. The exhaust pipe is connected to a muffler 05.
In the case where the exhaust pipe 01 is shaped and disposed in the above-described manner, the following disadvantages arise.
(1) There is a possibility that mud splashed by a front wheel is liable to adhere to the front end portion of the exhaust pipe, is positioned behind the front wheel. PA0 (2) Taking into consideration the foot rest attitude of a rider, generally at the level lower than the fuel tank, a large diameter portion of the exhaust pipe 01 is positioned in front of the fuel tank. PA0 (3) Consequently, in order to reasonably dispose the exhaust pipe 01 at a level lower than radiators 06, the sizes and mounting positions of the radiators 06 are restricted.